DEARBORN, Michigan (CNN) -- While all eyes were on Fred Thompson, the most heated exchanges during Tuesday's GOP presidential debate occurred between Rudy Giuliani and Mitt Romney, as they attacked each other's fiscal records.

Fred Thompson debates his fellow Republican presidential candidates for the first time Tuesday.

The debate, Thompson's first since he officially joined the Republican presidential race last month, involved nine GOP candidates and touched on trade, taxes and a range of economic and security issues.

"I've got to admit, it was getting a little boring without me, but I'm glad to be here now," Thompson said.

During the debate, sponsored by CNBC and the Wall Street Journal, Thompson was largely spared direct fire from the other candidates.

But Romney, a former governor of Massachusetts, and Giuliani, the former mayor of New York, continued the verbal sparring their campaigns have engaged in over the last few weeks.

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"It's baloney," responded Romney, who leads the polls in the key early voting states of Iowa and New Hampshire. "Mayor, you've got to check your facts."

Romney defended himself by saying he lowered taxes, not raised them as Giuliani charged, and said state spending in Massachusetts grew at a slower rate while he was governor than New York City's budget grew during Giuliani's tenure.

Thompson received one slight barb when Romney said how much the Republican debates reminded him of "Law and Order," the TV series in which Thompson starred.

"It has a huge cast, the series seems to go on forever, and Fred Thompson shows up at the end," Romney said.

Thompson responded, "And to think I thought I was going to be the best actor on the stage."

The former Tennessee senator survived a gotcha question, correctly identifying the prime minister of Canada as Stephen Harper.

He also was asked about the dangers of a weak U.S. dollar. "Danger of a weak dollar is that it will damage us internationally. We've got to have a strong dollar because of the creditors that we have there," he said. "Any president of the United States has to stand behind a strong dollar. The whole world needs to know that we are good for our obligations."

Thompson -- who has been fashioning himself as a straight-talking, outside-the-Beltway reformer, despite his decades as a lawmaker and lobbyist -- said he doesn't think "anybody believes anything coming out of Washington anymore."

"I think we need to tell them the truth -- that our security is on the line, that our economy is on the line, that our prosperity is on the line. We're going to have to do some things differently," he said. "Those are truthful things that the American people, I think, have an intuition about. We need to own up to it."

Thompson pushed one specific policy proposal likely to be controversial -- indexing increases in Social Security benefits to the rate of inflation, rather than growth in wages, for future retirees as a way to alleviate financial pressures on the retirement system.

"It wouldn't affect current or near retirement people, but for future retirees, instead of having nothing -- which is what they're headed for under the current situation that's unsustainable -- they would have protection," he said. "It would solve the problem for several years. It wouldn't solve it indefinitely, but it would give us a window of opportunity to get our arms around the problem."

Indexing Social Security to inflation rather than wages is strongly opposed by many Democrats, who argue it will result in sharply lower benefits.

Touching briefly on Iraq, Thompson offered limited criticism of the Bush administration's conduct of the war, saying "We didn't go in with enough troops, and we didn't know what to expect when we got there."

"But now, we're showing signs of progress," he said. "I think we've got to take advantage of the opportunities that we have there, now that we see a window of opportunity for things to turn around and us to stabilize that place and not have to leave with our tail between our legs."

At the end of his two-hour debut, Thompson was asked how the experience felt.

"Just like home," he said, drawing laughter. Then, he added, "I didn't say which kind of home."E-mail to a friend